Oxidizers with improved thermal stability and method of making same

ABSTRACT

Oxidizing compounds are provided which have improved thermal stability and which are particularly useful in explosive and propellant compositions. Such oxidizers are produced by making solid solutions of the oxidizer with at least one other compound. The solid solutions of particular interest for the purpose of this invention are ammonium perchlorate (NH4CIO4) and potassium perchlorate (KClO4), or ammonium perchlorate and ammonium nitrate (NH4NO3).

United States Patent Morrow 14 1 Jan. 2, 1973 s41 OXIDIZERS WITH IMPROVED 3,030,179 4/1962 McFarlm et a1. ..l49/46 x THERMAL STABILITY AND METHOD 3,148,946 9/1964 Griffith 1 9/46 X 3,166,450 1/1965 Kaufman... ..l49/46 OF MAKING SAME 3,173,756 3/1965 Griffith ..l49/46 X [75] Inventor: Scott 1. Morrow, Morris Plains, NJ. 3,269,879 8/1966 Stammler et al. ..l49/46 m1 Aeeigeee The Wee Seeeee er Ameeeee ee 33333332 21329 $312,231,331:111111111 125722 6,?

represented by the Secretary of the I Army Primary Examiner-Stephen J. Lechert, Jr. [22] Filed: April 21, 1971 Attorney-Harry M. Saragovitz, Edward J. Kelly, Herb tBl dA.V' t Ekk'l 211 App]. No.: 135,977 er er or r M r I [57] ABSTRACT it [52] U.S.Cl. ..l49/2,l49/46, 149/76, oxidizing compounds are provided which have 149/77 proved thermal stability and which are particularly [51] Int. Cl. ..C06b 1/04 useful in explosive and propellant compositions S h [58] Field of Search ..l49/46, 2, 76, 77, 40, 41 oxidizers are produced by making solid solutions f the oxidizer with at least one other compound. The [56] References Cited solid solutions of particular interest for the purpose of this invention are ammonium perchlorate (NH,CIO UNITED STATES PATENTS and potassium perchlorate (KCl0 or ammonium .8 /19 ay e X perchlorate and ammonium nitrate (NH,,NO 1,568,324 1/1926 Dehn ....l49l46 X 2,590,054 3/1952 Taylor et al. ..l49/46 X 8 Claims, 1 Drawing Figure PATENTEU m 2 I975 00 wmntxmmaiwk 00v 00m 00m OO INVENTOR, SCOTT l. MORROW 4 VMA OXIUDIZERS WITH IMPROVED THERMAL STABILTTY AND METHOD OF MAKING SAME The invention described herein may be manufactured, used and licensed by or for the Government for governmental purposes without the payment to me of any royalties thereon.

BACKGROUND OF THE INVENTION Prior Art It is generally known that many explosives and propellants contain oxidizers as one of their principal ingredients. It is also known that oxidizers, by their very nature, are thermally unstable and their use in explosive and propellant compositions frequently presents serious problems.

On the one hand, this thermal instability of oxidizers is a property which is not only desirable but in fact necessary for the manufacture of such explosives or propellants. Without such thermal instability, these oxidizers would lack the energy which makes them particularly useful for such applications, i.e., explosives and propellants. On the other hand, if they are too unstable thermally, they cannot, as a practical matter, be employed for such purposes. This is due to the fact that explosives or propellants which contain oxidizers with poor thermal stability cannot be safely stored, even at ambient temperatures, for any extended period.

Many attempts have heretofore been made to improve the thermal stability of such oxidizers for use in explosive and propellant mixtures. One approach has been to coat the oxidizer with a film of a more stable material, such as, for example, a plastic film. However, experience has shown that it is extremely difficult to coat such oxidizers with a uniform, adherent and stable coating. Furthermore, these oxidizers have a tendency to decompose, even at ambient temperatures. The gaseous materials released by such decomposition will diffuse through such coating materials and may cause them to rupture completely. Accordingly, this approach has not been too satisfactory in most instances.

Another approach has been to chemically coat or dope these oxidizers, in particulate forms. However, no suitable chemical or doping" agents have been found to be'satisfactory for the purpose of improving the thermal stability of these oxidizers.

Efforts have also been made to improve the thermal stability of such oxidizers by forming complexes thereof with certain organic compounds. However, the resulting complexes have been found to be equally unstable and decompose thermally even at ambient temperatures.

Another approach to this problem is discussed in US. Pat. No. 3.l47,l60 issued Sept. 1, 1964 to Walter C. McCrone. This patent discloses a method of desensitizing explosives containing ammonium perchlorate. The method described therein comprises coating ammonium perchlorate crystals with certain coating agents which form a solid solution with the ammonium perchlorate, the oxidizer employed in this patent. See Column 1, lines 3035. The coating agents disclosed in the aforementioned patent are sulfates, fluoroborates and certain compounds of gold, cesium, radium and thallium. These are not oxidizers themselves but form a solid solution coating with the ammonium perchlorate. See column 1, lines 41-46.

It is apparent from the description of the aforementioned patent that thermal stability of the oxidizer is improved by forming a protective coating thereon. These coatings do not afford the necessary thermal stability for reasons which were partly discussed, supra.

SUMMARY OF THE INVENTION The present invention is aimed at improving the thermal stability of oxidizers, particularly those oxidizers which are employed in the preparation of explosives or propellants.

This invention is also directed to a method of improving the thermal stability of oxidizers which are useful in explosive or propellant compositions.

In one particular aspect, the present invention is con cerned with providing such improved oxidizers in the form of solid solutions, and to a method of their preparation.

In one of its more specific aspects, the present invention is directed to a method of improving the thermal stability of ammonium perchlorate by making a solid solution thereof with potassium perchlorate.

These and other aspects of this invention will be more readily comprehended from the following detailed descriptions of the invention taken in connection with the accompanying drawing.

DETAILED DESCRIPTION OF THE INVENTION 1. Description of the Drawing In the drawing appended hereto, the thermal stability of pure NH CIO is compared with the thermal stability of a solid solution of NH C1O and KClO, in which the weight ratios of the former to the latter are approximately 3:1, 1:1 and 1:3, respectively. A more detailed explanation of this drawing will follow the description of the examples, infra.

2. Description of the Invention It has now been discovered that the thermal stability of oxidizers can be improved by making solid solutions thereof with certain specified materials to be hereinafter described. Such solid solutions can be employed in the manufacture of explosives and propellants, and such explosives and propellants can be stored at ambient conditions for extended periods of time, without the danger of thermal degradation of the oxidizers, until they are ready to be used for their intended applications.

Thus, it has been discovered that the thermal stability of NH C1O (a known oxidizer used in many explosives) can be improved by forming a solid solution of ammonium perchlorate with a compound which is isomorphous (i.e., has similar crystalline structure) with ammonium perchlorate. For example, it has been found that potassium perchlorate (KC1O is particularly suitable for forming a solid solution with NH C1O The resulting solid solution is more thermally stable than ammonium perchlorate and can be satisfactorily employed in explosive and propellant mixtures without the danger of decomposition during storage.

While not intending to be bound by any particular theory or mechanism, it is believed that improved thermal stability of the aforesaid solid solution is due to the fact that the radius of the potassium ion (K') is smaller than the radius of the ammonium ion (NI-1 i.e., 1.34 angstrom units as compared to 1.43 angstrom units.

.constituents,

Thus, the potassium ions can readily find their way into the crystal lattice of the solid solution of Nl-l ClO KCIO, and hence the resulting solid solution exhibits higher thermal stability than NH ClO alone.

From the aforesaid description, it is readily observed that compounds containing a common, but smaller ion than the ion contained in the oxidizer itself, can be employed to form a solid solution with the oxidizer with a resultant improved thermal stability of the oxidizer compound.

The term solid solution is employed throughout this application in its usual connotation, i.e., a homogeneous solution of one solid in another. This term, however, is also intended to include a dispersion of one solid in another such that the resulting mixture is homogeneous throughout. Thus, a solid solution of NH CIO :KCIO., always consists of these two components but varies only in the relative percentages of the compositions of these two constituents.

While in the aforementioned solid solution the two i.e., NH CIO and KCIO, are isomorphous, it has also been found that in certain instances, compounds which are not isomorphous with the oxidizer, in the usual sense, also form solid solutions therewith which have improved thermal stability. Thus, for example, some compounds which do not evidence isomorphism but which exhibit so-called kryptoisomorphism (i.e., hidden similarity in crystalline structure), are also capable of imparting improved thermal stability to the oxidizers by forming solid solutions therewith. Thus, any compound which forms a solid solution with the oxidizer and which improves its thermal stability is within the contemplation of this invention.

It must be pointed out also that the solid solutions which are formed in accordance with this invention are not necessarily limited to binary mixtures but may include ternary solid solutions as well. For example, potassium permanganate (KMnO which is isomorphous with both Nl-l ClO and KClO can form a ternary solid solution with these two compounds.

The method of improving the thermal stability of oxidizers useful in explosive and propellant compositions will now be illustrated with reference to NH ClO as the oxidizing compounds. The thermal stability of other oxidizers may be improved by following the method generally outlined herein for Nl-l ClO,,.

PREFERRED EMBODIMENT OF THE INVENTION The preferred method of improving the thermal stability of the oxidizer (Nl-l ClO comprises adding a solubility excess of NH ClO and KClO to a suitable solvent (e.g., water) in a glass container. Porcelain balls or other suitable grinding media are added to this solution and the container is then sealed and the resulting mixture is agitated while the glass container is maintained in a constant temperature bath. The mixture is agitated for about one week at a constant temperature of about 25 C. Mixed crystals (solid solution) of Nl-hClO. and KClO are formed in chemical equilibrium with the solution which is saturated with respect to both solutes, i.e., NH ClO and KClO,. When such chemical equilibrium has been reached, the mixed crystals of Nl-hClO-KCIO are separated from the solution by known techniques such as, e.g., filtration or centrifugation. The mixed crystals are thereafter dried in a vacuum oven, first at ambient temperature for a period of about minutes, and thereafter for an additional period of 4 hours and 30 minutes at slightly higher temperature, such as, e.g., at about 4045 C., until the mixed crystals are completely dehydrated. The anhydrous mixed crystals (solid solution) of Nl-l ClO -KClO may thereafter be ground to any desired particle size and used in explosive or propellant formulations.

A ternary solid solution of Nl-l ClO.,, KCIO, and KMnO, may also be prepared following the procedure heretofore described for the preparation of binary solution of NH CIO and KClO Since in both instances, the solution of these salts is agitated until a chemical equilibrium has been attained between the mixed crystals and the solution in which they exist, this procedure will hereinafter be referred to as the equilibrium method."

OTHER EMBODIMENTS OF THE INVENTION Another method of improving the thermal stability of an oxidizer (Nl-l ClO comprises preparing a saturated or essentially saturated solution of Nl-l,,ClO and KClO in water, or in any other suitable solvent. The solvent is then allowed to evaporate slowly and at an essentially constant temperature of 25 C. Mixed crystals of the aforesaid components are thus produced upon complete evaporation of the solvent. The mixed crystals may then be dehydrated and ground to the desired particle size as previously described in connection with the description of the equilibrium method.

Ternary solid solutions, such as e.g., solid solution of Nl-l ClO KCIO, and KMnO, may also be prepared in a similar manner. Since this method is based upon the evaporation of the solvent at essentially constant temperature, this method will hereinafter be referred to as the isothermal evaporation method."

In yet another method of improving the thermal stability of oxidizers, Nl-l ClO and ammonium nitrate (NH NO are mixed thoroughly in powder form and the resulting mixture is heated to a temperature of about C. or slightly higher. Ammonium nitrate melts at l69.6 C. while NH ClO does not. The latter compound does not have a melting point, but rather it decomposes at a temperature of about 400 C. Accordingly, when the mixture of these two compounds are heated as aforesaid, ammonium nitrate will be liquefied and the oxidizer, i.e., Nl-L,Cl0. will dissolve in the resulting liquid. When the ammonium perchlorate has been completely dissolved, the mass is cooled thereby forming mixed crystals (solid solution) of NH ClO and NH NO Since this method depends upon fusion of the two components, it will hereinafter be referred to as the thermal fusion method.

In the thermal fusion method, it is essential to avoid overheating of the mixture since otherwise gaseous material will be released as a result of decomposition of the NH,NO These gases will be trapped in the mixed crystals upon cooling hence lowering the density of the resulting solid solution. However, in the event that such gases are trapped in the mixed crystals, they can be removed by known techniques such as, e.g., vacuum melting of the mixed crystals with concomitant agitation in order to remove these gases. When no more gases are evolved, the mixture is allowed to cool in order to obtain the desired mixed crystals.

Again, as in the thermal equilibrium method, the resulting mixed crystals can be dried until they are anhydrous and thereafter ground to the desired particle size for use in explosives and propellant formulations.

Mixed crystals of NH NO and NH CIO may also be prepared by the equilibrium method and the isothermal evaporation method as previously described in connection with the formation of mixed crystals of NH ClO and KClO it must be pointed out that in the aforesaid description of the various methods of improving the thermal stability of oxidizers, the term mixed crystals and solid solution are used interchangeably to denote the same type of materials.

The present invention will now be further illustrated by the following examples.

EXAMPLE 1 This example illustrates the preparation of a solid solution of NH CIO and KClO in which the weight ratios of the two components are approximately 75 and 25 weight percent, respectively.

13.3327 grams of dried, pulverized triple recrystallized Nll l Cl O was charged to a glass flask containing 10.0693 grams of fresh deionized distilled water (containing less than one part per million NaCl conductivity equivalent) and three stainless steel balls each having an outside diameter of five-sixteenths of an inch. The

mixture was then agitated manually in order to thoroughly disperse the ammonium perchlorate in water. Thereafter, 3.3270 grams of dried, ground triple recrystallized KCIO was added and the mixture was once again agitated manually in order to thoroughly disperse the potassium perchlorate therein and more water was added until the water content in the flask was 16.6763 grams. The mixture was then thoroughly agitated and the flask was sealed without heating the content thereof. The flask was then immersed in a water bath maintained at a constant temperature of 25 C. 0.05 C. and the flask was agitated slowly (oscillated) for a period of one week.

At the end of this period, the content of the flask was transferred to a fritted glass filtration tube-receiver combination in which the receiver was connected to an aspirator. However, before the content of the flask was transferred, aliquot portions of the content of the flask were removed, diluted with water and analyzed for their ammonium and potassium ions by the Kjeldahl method and flame spectrophotometric method, respectively.

The remaining content of the flask was filtered, the material on the filter paper was dried to a constant weight for several hours in a vacuum oven at ambient temperature, and thereafter dried for an additional four hour period in the vacuum oven at 40 C. The resulting material (mixed crystals) contained 74.20 and 25.80 weight percent Nh.,Cl0, and KClO respectively.

The mixed crystals recovered in Example 1 were subjected to differential thermal analysis and compared with pure NH,,ClO.,. The results of this test are shown in the appended drawing which will be discussed, infra.

EXAMPLE 2 The procedure in this example was the same as in Example 1 except that 9.8935 grams of water and 9.8245 grams of Nl-hClO, were initially charged to the flask, followed by additional water (6.7910 grams) and 6.8248 grams of KClO The solid solution recovered in this example was found to contain 51.23 and 48.77 weight percents NH ClO and KClO respectively. The improved thermal stability of this solid solution is also illustrated in the appended drawing.

EXAMPLE 3 Again, the procedure followed in this example was the same as in the preceding two examples, the only difference being the relative amounts of the materials charged. Thus, 9.9385 grams of water and 5.8724 grams of NH CIO were added to the flask, followed by an additional 6.7346 grams of water and 10.8227 grams of KCIO... The solid solution recovered in this case contained 25.87 and 74.13 weight percents NH ClO and KClO.,, respectively. The improved thermal stability of this solid solution is also shown in the drawing.

Referring now to the drawings, four curves are shown which are labeled 1, 2, 3, and 4, respectively. Each label (as indicated by the legend in the drawing) corresponds to a particular composition. Thus, the curve designated by the numeral 1 corresponds to pure NH ClO and those designated by numerals 2, 3 and 4 correspond to the solid solutions obtained from Examples l, 2 and 3, respectively. These curves illustrate the thermal stability of the respective compositions.

As was previously mentioned, the thermal stabilities of the aforesaid compositions are determined by a differential thermal analyzer with which those skilled in the art are familiar. in this instrument, the desired composition is heated at a given temperature and the temperature rise is measured. This temperature rise (AT) is plotted against the temperature at which the composition was heated.

Ammonium perchlorate was used as the reference material in preparing these plots. As shown in the drawing, this compound evidences great thermal instability as is indicated by the very sharp increase in temperature rise at 400 C. and higher temperatures. On the other hand, the curves corresponding to the solid solutions obtained in the foregoing examples exhibit smaller temperature increase, hence indicating higher thermal stability.

Actually, the thermal stability of the aforesaid compositions may be determined by a comparison of the areas defined by said curves (also referred to as exotherms). Thus, for example, the area defined by the exotherm corresponding to Nh ClO is larger than the area defined by the exotherm defined by a solid solution of 74.20 percent NH.,C1O. and 25.80 percent KClO indicating that this solid solution has greater thermal stability than pure NH ClO The increased thermal stability of the other two solid solutions is also readily discernible from a comparison of the areas defined by their respective exotherms with the abscissa. Thus, from this drawing, it can be readily determined that a solid solution of 25.87 percent NH CIO and 74.13 percent KClO has greater thermal stability than the other three compositions.

While the present invention has heretofore been described with some degree of particularity, it must be emphasized that there are other methods which produce mixed crystals of the aforesaid components which are nevertheless within the scope of this invention. Thus, for example, activation of a mixture of NH ClO and KClO, with ultrasonic energy, colloid mill, ultrasonic disrupter or a shearing type stirrer all cause the formation of mixed crystals of the type described herein, i.e., mixed crystals having improved thermal stability.

Furthermore, while FIG. 1, supra, illustrates the improved thermal stability of mixed crystals of NH ClO- KClO as compared to NH ClO alone, similar improvement in thermal stability is observed when using mixed crystals of and NH ClO and NH NO What is claimed is:

l. A composition comprising a non-aqueous solid solution of ammonium perchlorate and potassium perchlorate.

2. A composition according to claim 1 containing in addition potassium permanganate.

3. A composition comprising a non-aqueous solid solution of ammonium perchlorate and ammonium nitrate.

4. A method of increasing the thermal stability of ammonium perchlorate which comprises dissolving the ammonium perchlorate and at least one compound capable of forming a solid solution with said oxidizer in a common solvent, said compound being selected from the group consisting of potassium perchlorate and ammonium nitrate, agitating the resulting solution until equilibrium is attained between the resulting solid solution and said solvent and recovering said solution from said solvent.

5. A method according to claim 4 wherein the solvent is removed essentially at isothermal conditions.

6. The method of claim 4 wherein said compound is potassium perchlorate.

7. A method of increasing the thermal stability of an oxidizer selected from the group consisting of ammonium perchlorate and potassium perchlorate which comprises mixing said oxidizer with ammonium nitrate, heating said mixture so as to completely liquefy said oxidizer thereby dissolving said ammonium nitrate to form a homogeneous solution of said ammonium nitrate in said oxidizer and cooling the resulting solution to obtain a solid solution of said oxidizer and said ammonium nitrate.

8. The method of claim 7 wherein said oxidizer is ammonium perchlorate. 

2. A composition according to claim 1 containing in addition potassium permanganate.
 3. A composition comprising a non-aqueous solid solution of ammonium perchlorate and ammonium nitrate.
 4. A method of increasing the thermal stability of ammonium perchlorate which comprises dissolving the ammonium perchlorate and at least one compound capable of forming a solid solution with said oxidizer in a common solvent, said compound being selected from the group consisting of potassium perchlorate and ammonium nitrate, agitating the resulting solution until equilibrium is attained between the resulting solid solution and said solvent and recovering said solution from said solvent.
 5. A method according to claim 4 wherein the solvent is removed essentially at isothermal conditions.
 6. The method of claim 4 wherein said compound is potassium perchlorate.
 7. A method of increasing the thermal stability of an oxidizeR selected from the group consisting of ammonium perchlorate and potassium perchlorate which comprises mixing said oxidizer with ammonium nitrate, heating said mixture so as to completely liquefy said oxidizer thereby dissolving said ammonium nitrate to form a homogeneous solution of said ammonium nitrate in said oxidizer and cooling the resulting solution to obtain a solid solution of said oxidizer and said ammonium nitrate.
 8. The method of claim 7 wherein said oxidizer is ammonium perchlorate. 